Thanks Eric yes that is one good example. I've been quite curious about when to play c5 in the classical caro endgame, something like this: Bologan-Dreev 2006: 3. Nd2 dxe4 4. Nxe4 Bf5 5. Ng3 Bg6 6. h4 h6 7. Nf3 Nd7 8. h5 Bh7 9. Bd3 Bxd3 10. Qxd3 e6 11. Bf4 Ngf6 12. O-O-O Be7 13. Kb1 O-O 14. Ne4 Nxe4 15. Qxe4 Nf6 16. Qe2 Qd5 17. Ne5 Qe4 18. Qxe4 Nxe4 19. Rhe1 Nf6 20. g4 a5 21. c3 Rfc8 22. f3 b5 23. Nd3 Nd5 24. Bg3 a4 25. a3 c5 26. Nf4 Nxf4 27. Bxf4 Rd8 28. dxc5 Bxc5 29. Rxd8+ Rxd8 30. Kc2 Kf8 31. Rd1 Rd5 32. Rxd5 exd5 33. Kd3 Ke7 34. Be3 Kd6 35. Bd4 1/2-1/2

Sitting on the black side it wouldn't immediately occur to me to push a and b pawns first before playing c5, as I would be worried that they would be weak. 

In the classical caro, Black aims to plays ..c5.
Sometimes it is not appropriate, and I can think of two scenarios why: (i) if Black has played Bg4xNf3 then ...c5 liberates the position for White's bishop pair, (ii) a4/a5 has been inserted and playing ...c5 weakens the b5 square.

Two recent examples:
Zhao Jun (2589) - Wang Hao (2737) CHN-chT 2013 1. e4 c6 2. Nc3 d5 3. d4 dxe4 4. Nxe4 Nd7 5. Nf3 Ngf6 6. Nxf6+ Nxf6 7. c3 Bg4 8. h3 Bxf3 9. Qxf3 Qd5 10. Qg3 g6 11. Be2 Bg7 12. O-O O-O 13. Bf3 Qd7 14. Re1 a5 15. Bg5 a4 16. a3 Ra5 17. Re2 Qf5 18. Bf4 e6 19. Bc7 Raa8 20. Rae1 Qb5 21. h4 Rfe8 22. Be5 Nd7 23. Bd6 h5 24. Be5 1/2-1/2

Zahar Efimenko (2651) - Pavel Eljanov (2707) Kiev 2013 1. e4 c6 2. d4 d5 3. Nc3 dxe4 4. Nxe4 Bf5 5.Ng3 Bg6 6. N1e2 Nf6 7. Nf4 Nbd7 8. Bc4 Qc7 9. c3 e6 10. O-O Bd6 11. Qf3 O-O 12. Bb3 a5 13. a4 Bxf4 14. Qxf4 Qb6 15. Bc4 Rfe8 16. b3 Nd5 17. Qd2 e5 18. dxe5 Nxe5 19. Bxd5 Rad8 20. Qd4 Qc7 21. c4 cxd5 22. cxd5 Bd3 23. Bg5 f6 24. Rfc1 Qf7 25. Bf4 Qxd5 1/2-1/2

For pedagogical purposes I am looking to collect examples where Black avoids ...c5. Are there any other instructive examples? I seem to recall some old lines (by Larsen?) where Black just goes ...a5/...a4/...a3 but don't think this is a common way to play anymore.